A conventional hearing aid comprises a microphone, a hearing aid processor for performing hearing aid processing on the sounds collected by the microphone, a receiver for outputting the output signal of this hearing aid processor as an acoustic signal, a memory for storing a voice message, a voice reproducer for reproducing this voice message, a battery for supplying electrical power to these components, and a voltage monitor for monitoring the voltage of the battery.
When the voltage matches a preset condition, a voice message stored in the memory is reproduced by the voice reproducer. The reproduced voice message is supplied to the receiver after being added to the output signal of the hearing aid processor (see Patent Citation 1, for example).
Consequently, the user can be alerted by voice that it is time to replace the battery when the battery voltage has dropped.